circleCollision

//whether a circle and a rectangle collide
bool circleCollision(const Location &center, double radius, const SDL_Rect &rect){
   // test 1 && (test 2 || test 3)

   double
      left = rect.x,
      right = left + rect.w,
      top = rect.y,
      bottom = top + rect.h,

      centerX = center.x,
      centerY = center.y;

   //test 1: the rectangles must collide, and
   if (centerX - radius > right ||
       centerX + radius < left ||
       centerY - radius > bottom ||
       centerY + radius < top)
      return false;

   //test 2: the center must be between the left-right or top-bottom edges of the rectangle, or
   if (centerX > left && centerX < right) ||
       centerY > top && centerY < bottom)
      return true;

   //test 3: at least one corner must be within circle
   if (distance(top, left, centerX, centerY) < radius ||
       distance(top, right, centerX, centerY) < radius ||
       distance(bottom, left, centerX, centerY) < radius ||
       distance(bottom, right, centerX, centerY) < radius)
      return true;

   return false;
}